In a conventional mobile communications network, a core network entity needs to be used when a terminal performs data communication. Therefore, when the terminal loses network coverage, the terminal cannot access the network to implement communication. By using a ProSe (Proximity Services, proximity services) technology, two terminals can implement device-to-device short range communication without using a core network entity. In this way, a terminal within network coverage may implement, by using the ProSe technology, short range communication with a terminal losing network coverage, thereby implementing a function of a relay terminal. In the prior art, a relay terminal may provide a relay service for a group of remote terminals. When data is sent over a network to a remote terminal losing network coverage, data transmission efficiency can be improved in a multicast manner. In this case, data exchange between the relay terminal and the remote terminal is implemented in a broadcast or multicast manner, so that the relay terminal can relay and forward data for a group of remote terminals in a group communication manner. Therefore, the remote terminal losing network coverage can receive network data by using a relay function of the relay terminal within network coverage.
However, if a relay terminal selected by a remote terminal is not in a same communication group as the remote terminal, the relay terminal does not have information about a communication group to which the remote terminal belongs. Therefore, the relay terminal cannot implement broadcast or multicast communication with the remote terminal, and further cannot relay or forward data for the remote terminal.